The ultrafast carrier dynamics of GaAs(1 0 0) surfaces passivated with different sulfide solutions is studied by time-resolved measurements of infrared absorption using the femtosecond visible-pump infrared-probe technique. After passivation of n-GaAs(1 0 0) surface with the solution of ammonium sulfide in 2-propanol the three-fold decrease of the surface recombination velocity is observed. The treatment of the n-GaAs(1 0 0) surface with the aqueous sulfide solution has a smaller impact on the surface recombination velocity. The different effect of aqueous and alcoholic sulfide solutions on the efficiency of surface passivation is caused by the different mechanisms of charge transfer at the semiconductor/solution interfaces. (C) 2012 Elsevier B. V. All rights reserved.